1. Field of the Invention
The present invention relates to an automatic focusing camera. More particularly, the invention relates to a camera capable of performing a highly precise focusing by providing detecting means on the lens side for detecting the driving amount of a focusing optical system.
2. Related Background Art
FIG. 12 illustrates an example of a conventional automatic focusing camera. In the camera shown in FIG. 12, an exchangeable photographing lens 41 is mounted on the body 42, and an objective image passing through the photographing lens 41 is detected by a photoelectric conversion section 45 through a main mirror 43 and a sub-mirror 44. The output from the photoelectric conversion section 45 is inputted into a focus detecting means through an A/D converter incorporated in a microcomputer (hereinafter referred to as CPU) 50 to obtain a defocus amount. In the meantime, lens data per se is inputted into the body side from the photographing lens 41 through lens data transmitting/receiving controllers 48 and 49 on the lens side and body side respectively, and a calculating means in the CPU 50 works out a required driving amount for a motor 52 on the basis of this lens data per se and the defocus amount obtained from the aforesaid detecting means. The data indicating the required driving amount is applied to one of the inputs of the coincidence detector in the CPU. To the other input of the aforesaid coincidence detector, signals corresponding to the driving amounts from a photointerrupter 54 provided in the body 42 and a pulse counter 55 are inputted in order to obtain the signal which corresponds to the driving amount of the motor 52. The coincidence detector compares this signal corresponding to the driving amount and the signal corresponding to the required driving amount obtained from the aforesaid calculating means. Thus, a signal corresponding to the difference between them is generated. The signal thus obtained is applied to the motor 52 through a motor driver 56. In this way, the motor 52 drives the focusing optical system L2 in the photographing lens 41 side through a coupling member 57 between the camera 42 and the lens 41 to perform focusing.
However, in the above-mentioned conventional camera, as the driving amount of the focusing optical system L2 is obtained by the pulse obtainable from the photointerrupter 54 mounted on the motor driving shaft, there have been encountered the problems given below.
(1) It takes a constant time before the defocus amount is obtained after the signal from the photoelectric conversion section 45 has been inputted into the focus detecting means. If a focus detection is performed while the focusing optical system L2 is being driven, the position of the focusing optical system L2 is dislocated from a position at which to begin obtaining the focus amount by a portion equivalent to such a constant time required for obtaining the defocus amount. Therefore, if the focusing optical system L2 is driven as it is from the result of the focus detection, the focusing optical system L2 cannot be stopped at a position where the focusing optical system has come into focus.
(2) Due to the mechanical gaps existing in the gears and others between the motor driving shaft in the camera body 42 side and the focusing optical system L2, the pulse numbers obtainable from the photointerrupter 54 do not coincide with the actual position of the focusing optical system L2 perfectly. Particularly, when driving pulses are output to reverse the driving direction, there are some cases where the focusing optical system L2 is not driven because of the backlashes of the gearing, coupling member 57, and the like. It is therefore necessary to use highly precise gearing and coupling member 57 for positioning the focusing optical system L2.
(3) When the focusing optical system L2 should be driven for a precise amount to be in focus in particular, it is preferable to drive the motor at a low speed for several pulses to enable the focusing optical system L2 to be positioned accurately.